SpaceShipOne has a wet mass of about 3.5 tonnes (if I remember correctly), around 50% of which is fuel. By comparison, to launch an equal dry weight (basically the flight controls, wings, and passengers) into orbit would require approximately 20 tonnes worth of fuel. You point me to a plane which can easily carry 20 tonnes of highly volatile rocket to a sufficient height to be worthwhile, and I'd be impressed.

Be impressed The Antonov An-225 Mriya has a payload of 250-275 tonnes, internally or externally mounted. It was mooted as the launch stage for the MAKS shuttle.

However, that does not necessarily mean it is practical. In my opinion, there are greater and smarter people than us working on launch technology, and that only one group of them decided to use air-borne launch says something about it.

Only one team that uses air-launch - right. But there other teams working on single stage concepts according to their websites. Their vehicle are planes using rockte engines - these concepts simly don't require air launches. One of this teams recently announced to be ready in 2007.

And Suborbital Corporation in Russia had in mind to use air-launch too. But they are suffering by lack of financial ressources as I remember.

However, that does not necessarily mean it is practical. In my opinion, there are greater and smarter people than us working on launch technology, and that only one group of them decided to use air-borne launch says something about it.

Not really. It shows us that rocket engineers build rocket-shaped things, and airplane engineers (like Rutan) build airplane-shaped things, and seldom do the two meet

There have been several design attempts by very clever people for air-launched orbital craft (MAKS, Sanger, the early Space Shuttle designs). These failed for budgetary and political reasons as much as technical ones.

However, that does not necessarily mean it is practical. In my opinion, there are greater and smarter people than us working on launch technology, and that only one group of them decided to use air-borne launch says something about it.

Yeah. The only team to fly a fullscale vehicle and in the process WIN the X-Prize.

Robotic and human lunar expeditions.
Sustained, long-term robotic and human exploration of Mars.
Robotic exploration across the solar system.
Advanced telescope searches for Earth-like planets and habitable environments.
Development of an exploration transportation system.
Completion of the International Space Station and focusing its use on supporting space exploration goals.
Exploration of the Universe.
Exploration of the dynamic Earth system.
Exploration of the Sun-Earth system.
Advanced aeronautical technologies for next-generation aviation systems.
Using NASA missions inspire, motivate, and educate.
Utilization of nuclear systems for the advancement of space science and exploration.
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